%%
%% The LaTeX Companion, 3ed
%%
%% Example 6-3-8 on page I-453 in "Managing tables with wide entries".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{135.0pt}
%StartShownPreambleCommands
\usepackage{array,calc}
%StopShownPreambleCommands

\begin{document}
\begin{tabular*}{\widthof{This is a wide heading line}
                 + 2\tabcolsep}
                { !{\extracolsep{4in minus 4in}} ccc}
\multicolumn{3}{c}{This is a wide heading line}     \\
C1 & C2 & C3 \\ 2.1 & 2.2 & 2.3 \\ 3.1 & 3.2 & 3.3
\end{tabular*}
\end{document}
